Field of the Invention
The present invention relates to an inrush current inhibiting circuit.
Description of Related Art
In the case of turning on a power source of an apparatus (load), a large-capacity current (inrush current) exceeding a steady current may flow from the power source to the load. Since the inrush current may adversely affect each place of the apparatus, an inrush current inhibiting circuit for inhibiting the inrush current is known.
For example, Patent Reference 1 discloses an inrush current inhibiting circuit using a principle of a step-down chopper circuit. This inrush current inhibiting circuit is a circuit for outputting electric power from a pair of output terminals to a load using a DC power source as an input. The inrush current inhibiting circuit includes a series circuit of a coil and an FET between a positive electrode of the DC power source and one output terminal. The other output terminal is connected to a ground of the DC power source, and a reflux diode is connected in inverse-parallel with the coil. Also, a capacitor is formed between one output terminal and the ground of the DC power source.
In this inrush current inhibiting circuit, a control voltage is outputted from a driving circuit to a gate of the FET according to a high-frequency pulse signal, and switching operation of the FET is performed according to this control voltage. When an input voltage switched by the FET is applied to the coil, a current flows through the FET for only an on period (conduction period) of the FET, and the capacitor is charged. For a non-conduction period of the FET, charging of the capacitor is stopped and a current of the coil is decreased while circulating through the coil and the diode. The capacitor is charged every high-frequency pulse signal through such a cycle. In this case, a peak value of the charging current becomes small gradually and becomes zero at the completion of charging of the capacitor.
Patent Reference 1 JP-A-8-275383
According to a related art, a technique disclosed in Patent Reference 1 uses a coil as an inductor. In an apparatus using a large current, a large-diameter electric wire is used and the coil must be wound by an electric wire, with the result that there is a problem of upsizing a circuit. Also, in the case of a large-diameter electric wire, winding work of the coil requires time and effort, with the result that there is a problem of complicating work of manufacture.
Also, in an inrush current inhibiting circuit, withstand power characteristics of a switching element are selected on the premise of a peak current value of an inhibited inrush current. In the case of using a switching element with a large power capacity, a peak of the inhibited inrush current can be permitted sufficiently. On the other hand, since a current value when the inrush current attenuates is sufficiently smaller than the peak current value, a large difference is caused between both of the current values. As a result, there is a problem that the power capacity of the switching element cannot be utilized sufficiently.